A thin and high-strengthened material is used for parts of an automobile, for example, for satisfying both safety and economic purposes. A hot pressing (die quenching or hot forming) method, in which a heated steel plate is pressed by press-dies of low temperature and quenched, is known for a purpose of obtaining such a material. The method is practiced as follows. A steel plate is heated to the austenitizing temperature or more and then rapidly cooled by press-dies to quench the steel plate at the same time of its shape forming.
As a heating method for the hot pressing method, a method is known such as an electric (conduction) heating method or a method using a block heater, which can heat a material rapidly, as well as a furnace heating method. Patent Document 1 discloses a technique using a near infrared radiation heater as a heating furnace for hot pressing of parts of an automobile. Patent Documents 2 and 3 disclose a technique using infrared radiation for supplementary heating in a very small area of an electronic circuit part.
Patent Document 4 discloses a heating furnace for a work inside of which is divided into regions and each region can be heated at different temperature.    [Patent Document 1] Japanese Patent Kokai Publication No. JP2007-314874A    [Patent Document 2] Japanese Patent Kokai Publication No. JP-A-5-45607    [Patent Document 3] Japanese Patent Kokai Publication No. JP2001-44618A    [Patent Document 4] Japanese Patent Kokai Publication No. JP2002-241835A